Next generation multimedia wireless communication system is standardized to provide an efficient connection between a wire communication network and a wireless communication network and to provide an integrated service beyond simple wireless communication services such as mobile communication systems of the previous generation. Link adaptation may be employed to efficiently use a wireless link. Typically, the link adaptation includes a power control scheme and an adaptive modulation and coding (hereinafter referred to as “AMC”) scheme. The power control scheme is a method to maintain transmission quality by controlling the power according to the state of the wireless link. The power control scheme is an efficient method in a system that is responsible for ensuring link quality under a fixed transmission rate such as voice services.
However, since multimedia data require various transmission rates, various transmission qualities, etc. according to the kinds of services, a new link adaptation of a concept different from existing voice-based services is required. The AMC scheme is an efficient link adaptation scheme for transmitting multimedia data, which adapts the transmission rate, not the transmission power, to channel environments.
Since the AMC scheme transmits data based on an appropriate transmission rate according to characteristics of the channel, the transmission power is fixed and the transmission rate is determined by an AMC level (also called a modulation and coding scheme (MCS) level). The AMC level is a level with respect to a predefined modulation and coding scheme. For example, high speed downlink packet access (HSDPA) supports a variety AMC levels using quadrature phase shift keying (QPSK), 16-quadrature amplitude modulation (16-QAM) and by efficiently puncturing a turbo code with a code rate of 1/3.
The AMC level is determined based on a carrier to interference and noise ratio (CINR), or based on a signal to interference ratio (SIR), in which a level showing the highest efficiency is selected. That is, under conditions where the channel environment is poor, QPSK having a low modulation index and a powerful channel coding scheme are used. Whereas, under conditions where the channel environment is good, a high modulation level and a low channel coding scheme are used. To support the AMC scheme, it is necessary that a base station should know information regarding the received CINR of a mobile station. In order to report the reception quality of the mobile station to the base station, channel quality information regarding the channel state is used.
Hereinbelow, downlink means communication from the base station to the mobile station, and uplink means communication from the mobile station to the base station. In general, the base station allocates radio resources to the mobile station. The radio resources become uplink resources on an uplink and downlink resources on a downlink. The radio resources allocated to the mobile station may be distributed in a frequency domain or in a time domain.
When the base station transmits a downlink frame to the mobile station, it is necessary that the base station should inform the mobile station of the AMC level of the frame at every frame. However, the channel environment is unlikely to be changed drastically, except for the case where the mobile station moves at high speed. It may be unnecessary signaling under limited radio resources that the base station fully informs the mobile station of the AMC level at every frame (full AMC level) even in the above case. Especially, since the AMC levels are different between the respective data regions or control regions included in the frame, the full AMC level may act as a higher overhead in the case where the AMC levels should be differently set according to the respective regions.
Thus, a method that can reduce the amount of radio resources used as the AMC levels is required.